1. Field of the Invention
The present invention relates generally to mixers for processing materials in a multitude of fields such as chemistry, medicines, electronics, ceramics, foods, and feed. More specifically, the present invention relates to a planetary mixer in which multiple frame-shaped blades are configured to undergo planetary motion within a tank, such as a vessel or a stirring tank, by which solid/liquid type treatment materials can be subjected to various treatment operations, including blending, mixing, kneading, mixing and kneading, and dispersion treatments.
2. Background Information
Operations such as mixing, kneading, mixing and kneading, and dispersion treatments of solid/liquid type treatment materials, of from a low viscosity to a high viscosity up to 3,000 Pa·s regardless of the oiliness or aqueousness of the materials, have been mainly treated in a batch system by a planetary mixer in which plural frame-shaped or rectangularly shaped blades undergo orbital and rotary movement (i.e., planetary movement) within a tank. Such type of planetary mixer includes, for example, a biaxial mixer which has two frame-shaped or rectangularly shaped blades, a triaxial mixer which has three frame-shaped blades, a mixer having two frame-shaped blades and one turbine blade, or a quad axial mixer having two frame-shaped blades and two turbine blades.
During a mixing and kneading operation using the frame-shaped blades of a planetary mixer, dispersion is carried out by shearing stress applied by rotation of the blades to the treatment materials flowing between the blades and an inner wall of a tank. More specifically, the steps of this operation are conducted similarly to those for the operation of roll mills. Namely, when an edge portion formed on an outer side of a vertical side portion of the frame-shaped blade comes close to the inner wall of a tank, treatment materials entering a gap between the blade and the inner wall of the tank are compressed between the blade edge portion and the inner wall of the tank. Then, the treatment materials between the edge portion of the blade and the inner wall of the tank are subjected to shearing by the shearing stress generated by the rotation of the blade. Finally, when the edge portion of the blade moves away from the inner wall of the tank, the treatment materials are released and expand. Since the dispersion operation with the roll mill is conducted through each of compression, shearing, release and expansion steps, the step caused between the frame-shaped blade and the inner wall of the tank is considered the same as the dispersion step by the roll mill.
The frame-shaped blades and the tank are constructed in various fashions depending on the particular purpose. For example, as a frame member of a frame-shaped blade for the planetary mixer described in JP-A-2000-271464, the upper portion of a vertical side portion of the blade has a straight shape, the lower portion of the vertical side portion of the blade curves in an arcuate shape towards a bottom portion, and the curved portion is connected to a bottom side portion of a hemispherical frame member in series. In this frame member, a plate-shaped stirring tool is disposed. Further, the tank has a cylindrical side wall, and its bottom face has no corner with an acute angle, and the entire configuration of the tank is one which curves into a substantially bowl-like shape corresponding to the bottom side portion of the frame member. In JP-A-2000-271464, the bottom face of this tank is similar to that of a trough of a twin-barrel type kneader as viewed in cross-section.
In the case of a kneader, the trough is formed in a substantially box-like shape, the kneader blade extends in a horizontal direction along the bottom face of the trough, and the rotation of the kneader blade causes the treatment materials to flow towards a large arcuate face at the bottom of a tank. Accordingly, high viscosity treatment materials can be efficiently mixed and kneaded by compression, shearing and release of the treatment materials between the curved face of tank and the kneader blade similarly to the case relating to the operation of the roll mill.
On the other hand, in a case of the frame-shaped blades of the planetary mixer, the blade shaft extends in a direction substantially perpendicular to the bottom face of the tank and rotates in a circumferential direction of the tank. Therefore, the vertical side portion of the frame-shaped blade and the curved portion on the bottom side portion of the blade do not cause the treatment materials to flow towards the bottom face of the tank. Accordingly, the shearing force to be applied from the curved portion of the blade to the treatment materials is not sufficiently transmitted, and the shearing force per unit area is not sufficiently large. Accordingly, in a case of a planetary mixer in which the bottom side portion of the frame-shaped blade and the bottom face of the tank are formed in a large curved form as described above, it is difficult to apply a strong shearing action to the treatment materials throughout the entire tank, and this mixer is often used for stirring and blending treatment materials having a low viscosity.
In another planetary mixer described in JP-A-9-267032, a tank has a cylindrical side wall and a flat plate-like bottom part, and the corners of a bottom face of the tank are formed with a right angle. A frame-shaped blade has a straight, vertical side portion extending along the side wall of the tank, and a straight bottom side portion extending along the bottom plate of the tank and connected to a lower portion of the vertical side portion at a right angle. In this case, when the frame-shaped blade rotates, since an edge face formed on an outer side face of the vertical side portion of the blade moves in close to an inner wall of the tank, the treatment materials having a high viscosity are caused to flow between the edge face of the vertical side portion of the blade and the inner wall of the tank and are applied with shearing stress. At the same time, between the bottom side portion of the blade and the bottom face of the tank as well, the treatment materials entering the space between the bottom side portion of the blade and the bottom face of the tank are applied with shearing stress for dispersion treatment by orbital and rotary movement of the blades. As a result, it is possible to conduct efficient mixing and kneading of the high viscosity treatment materials within the tank. In such dispersion action, in the case of a batch system, the application of shearing stress to the treatment materials between the frame-shaped blade and the inner wall of the tank or the stirring tank is non-continuous. Furthermore, in a mixing and kneading machine of which the frame-shaped blades have a planetary motion track, the application of such shearing stress is two times per one rotation of the frame-shaped blade.
As described above, in order to effect the mixing and kneading action adequately throughout the tank between the inner face and the bottom face of the tank, it is preferred that the blade extend to such a position where its straight vertical side portion reaches close to the bottom face of the tank, the intersection of the vertical side portion and the bottom side portion of the blade is formed at a right angle, and the corner of the bottom face of the tank is also formed at a right angle as described in JP-A-9-267032. However, in such a structure, the flowability of the treatment materials is poor in the vicinity of the right angle corner on the bottom face of the tank. As the result, the shearing rate and shearing stress become uneven and the treatment materials tend to gather around the corners or the like of the tank, whereby material in the form of a powder at the time of charging of the treatment materials or material at the time of mixing and kneading tends to adhere or fix to the corners of the tank. Particularly, a situation where a treatment material having a high viscosity is subjected to strong kneading will be explained below.
In one example, as shown in FIG. 5A, some of the material, denoted by C, often adheres to the corner on the bottom face of a tank T or to the inner face of the bottom side portion of a blade B. Accordingly, it becomes necessary to stop the mixing and kneading operation to allow the adhered material (contamination) C to be scraped. If the mixing and kneading operation is continued without scraping the adhered material C, partial aggregate of powder, such as hard agglomerates, tends to result in a dilution step after strong kneading, and the agglomerates are incorporated during the dilution, thereby deteriorating the quality of the treatment materials subjected to the dispersion treatment.
As mentioned above, when the material adheres and fixes to the corners at both ends of the bottom side portion of the frame-shaped blade and the corners on the bottom face of the tank, it is required to stop the mixing and kneading operation and to scrape the adhered material on the blade or the inner bottom portion of the tank. Not only is such scraping operation by workers dangerous, particularly in a case of the material adhered or fixed to the corners on the bottom face of the tank, but the scraping operation is also difficult and cumbersome, whereby hard agglomerates are likely to be incorporated during the dilution. Furthermore, since such scraping operation is necessarily conducted during the mixing and kneading operation, the mixing and kneading operation cannot be continuously carried out. Additionally, since an opening portion of the tank is opened during the scraping operation, it becomes impossible to tightly close the tank until completion of the mixing and kneading operation. In a case where a volatile organic solvent is used for the mixing and kneading operation, problems of environmental pollution may sometimes be caused by opening the tank.